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Hurricane Sandy Looks More Likely to Slam Eastern U.S.

Published: October 24th, 2012

Hurricane Sandy made landfall in Jamaica on Wednesday afternoon, and it is increasingly likely to turn into a massive — potentially even historic — storm with the potential to spread hazards ranging from coastal flooding to high winds across a wide area from the Carolinas northward to New England. Parts of the East Coast could start feeling the effects of Sandy as early as Saturday, and forecasters are beginning to urge people to start making preparations for severe weather, in case the computer models are correct and the storm does fail to turn harmlessly out to sea.

The afternoon run of the European model shows an intense hybrid storm making landfall in the Mid-Atlantic states.Click to enlarge the image. Credit: Weatherbell Analytics

During the past 24 hours, the models have come into better agreement about how Sandy will interact with several unusual weather features. Those converging events include a large dip in the jet stream into the eastern U.S., a powerful subtropical jet stream moving across the southern U.S., a massive area of high pressure that will be parked over northeastern Canada and southwestern Greenland, and a storm in the Central Atlantic. These features may help steer Sandy right into the Mid-Atlantic or New England.

As Sandy moves northward away from the Bahamas, it will come into contact with powerful jet stream winds that will be transporting much colder air into the Midwest and East. That is expected to add more energy to the storm and help it undergo a complex transition from a tropical weather system into a massive hybrid storm that more closely resembles an intense nor’easter. This is not good news, since nor’easters tend to have larger wind fields than most hurricanes, and can produce very similar impacts.

If Wednesday's computer model solutions turn out to be correct — and they may not — then Sandy (or the hybrid version of it), may bring large-scale coastal flooding, heavy rains, inland snows (yes, snow), and damaging winds to much of the eastern seaboard from North Carolina all the way up to Maine sometime during the Sunday-to-Wednesday timeframe.

A storm of that scope and magnitude striking the heavily populated Northeast coastline could cause a billion dollars or more in damage. Because of a full moon, tides will be at their highest levels for the month, so the threat of coastal flooding is particularly acute, given projections of onshore winds that could be as high as 60-plus mph.

This map clearly shows the unusual area of high pressure over Greenland which is forecast to block Hurricane Sandy and help force it northwestward into the East Coast.Click to enlarge the image. Credit: Weatherbell Analytics.

The National Weather Service forecast office in Philadelphia issued a briefing on Wednesday for emergency managers, warning that the odds have increased that the storm will impact the region. While stressing that the storm may still take a different track, forecasters said it may have an unusual combination of tropical rainfall, owing to Sandy’s beginnings as a tropical weather feature, and a large wind field that will cause major coastal flooding. “The storm will be slow moving. This worsens the impact for coastal flooding as it will affect multiple high tide cycles,” the briefing said.

The overall weather pattern is what is especially concerning to forecasters. While the ultimate destination of the storm may still change, it is looking more and more likely that Sandy won’t turn harmlessly out to sea after battering Jamaica, Cuba, the Bahamas, and southeastern Florida. Normally, hurricanes that form in Sandy’s location do head seaward, particularly in October, when strong cold fronts moving off the East Coast tend to sweep tropical weather systems away from the mainland. In fact, there may only have been a couple of cases in the historical record dating back to the 19th century when a hurricane took a track in October similar to the one Sandy may ultimately follow.

The high pressure area near Greenland, in particular, may act as a block (it's technically known as as a “blocking high”), which may help prevent Sandy from moving out into the open ocean. While it is not unusual to have a high pressure area in that location, its intensity is striking for this time of year. As Jason Samenow of the Capital Weather Gang wrote, the North Atlantic Oscillation, which helps measure this blocking flow, “is forecast to be three standard deviations from the average — meaning this is an exceptional situation.”

Recent studies have shown that blocking patterns have appeared with greater frequency and intensity in recent years, which some scientists think may be related to the loss of Arctic sea ice as a result of global warming. The 2012 sea ice melt season, which just ended one month ago, was extreme, with sea ice extent, volume, and other measures all hitting record lows. The loss of sea ice opens up large expanses of open water, which absorbs more of the incoming solar radiation and adds heat and moisture to the atmosphere, thereby helping to alter weather patterns. Exactly how weather patterns are changing as a result, however, is a subject of active research.

Here’s how the National Weather Service’s Hydrometeorological Prediction Center described the upcoming weather setup in a discussion on Wednesday, “THE ENTIRE ATLANTIC BASIN SEEMS DESTINED TO BECOME DOMINATED BY BLOCKY HIGHS AND LOWS, WITH DECREASING WIGGLE ROOM FOR EVEN LARGE FEATURES LIKE SANDY. THE BLOCKING IS KEY TO THE OPPORTUNITY FOR THE INTERACTION BETWEEN THE ATLANTIC STORM OF TROPICAL ORIGIN AND THE NORTH AMERICAN VORTEX OF POLAR ORIGIN.”

The blocking high, along with other features in the North Atlantic, should allow Sandy to come into contact with a polar air mass that will be moving southeastward out of Canada, into the Midwest and the East Coast. And that would add considerable energy to the storm.

Stay tuned to Climate Central for continuing coverage of the East Coast storm threat.